1. Field of the Invention
The present invention relates to a visual acuity examination apparatus for examining the visual acuity of an examinee, or an eye of the examinee, by presenting optotypes to the examinee.
2. Description of Related Art
There have been known visual acuity examination apparatuses for estimating the visual acuity of an examinee by sequentially presenting a plurality of optotypes for different visual acuity values (visual acuity levels or scales) to the examinee, or an eye of the examinee, and determining the visual acuity of the examinee based on whether the examinee could see (distinguish) or not the presented optotypes. Heretofore, the visual acuity examination apparatus of this type would generally perform a visual acuity examination by the use of optotypes expressed in decimal values for visual acuity.
However, the optotypes expressed in the decimal visual acuity values differ in size difference according to visual acuity values, and therefore accurate estimation could not be executed. To be more specific, in the decimal visual acuity values, the improvement in visual acuity from 0.2 to 0.3 and the improvement from 0.9 to 1.0 are both considered as the improvement of one level of visual acuity. However, if expressing in visual angle, the increase from 0.2 to 0.3 corresponds to 1.5 times the visual angle, while the increase from 0.9 to 1.0 corresponds to about 1.1 (1.0/0.9) times. Therefore, it would be difficult to make the same estimation in the above cases.
In judgement of the visual acuity, if five optotypes for the same visual acuity value are used, the maximum value among the visual acuity values of the optotypes to which three or more right answers are given (i.e., the largest value in decimal visual acuity values) is directly regarded as the visual acuity value of the examinee (the examinee""s eye). Consequently, the estimation would be rough and insufficient for the ophthalmologists and the like to confirm treatment results and correction results.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a visual acuity examination apparatus capable of easily and simply obtaining and estimating the visual acuity of an examinee""s eye.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a visual acuity examination apparatus for examining a visual acuity of an examinee by presenting an optotype to the examinee, the apparatus including: an optotype presenting unit which selectively presents at least one of a plurality of comparison optotypes expressed in geometrical series, the optotypes being provided to be plural in number for each visual acuity value; an input unit with which a distinction answer of the examinee with respect to the presented optotype is input; a storage unit in which an examination program which sequentially determines an optotype to be next presented based on whether the distinction answer with respect to the presented optotype is right or wrong is stored; a control unit which controls the optotype presenting unit in accordance with the examination program; and a processing unit which determines a visual acuity value of the examinee from a percentage of right answers in the distinction answers with respect to an optotype for a visual acuity value.
According to another aspect of the present invention, there is provided a visual acuity examination apparatus which switches and displays an optotype in a screen, the apparatus including: an optotype disc plate on which a plurality of charts each provided with one optotype or a plurality of optotypes are formed in a circle, the plurality of optotypes being configured in one line or three line in the chart; a mask disk plate on which a plurality of masks for presenting one optotype or at least a part of the optotypes formed on the chart; and a rotating unit which individually rotates the optotype disc plate and the mask disc plate, thereby to selectively present the optotype.
According to another aspect of the present invention, there is provided a visual acuity examination apparatus for examining a visual acuity of an examinee by presenting an optotype to the examinee, the apparatus including: an optotype presenting unit which selectively presents at least one of a plurality of comparison optotypes expressed in geometrical series, the optotypes being provided to be plural in number for each visual acuity value; an input unit with which a distinction answer of the examinee with respect to the presented optotype is input; a storage unit in which an examination program which sequentially determines an optotype to be next presented based on whether the distinction answer with respect to the presented optotype is right or wrong is stored; and a control unit which controls the optotype presenting unit in accordance with the examination program.